1. Field of the Invention
The present invention relates to a pyran derivative, and more particularly such a pyran derivative that exhibits long wavelength light. Further, the present invention relates to a light-emitting element containing the pyran derivative.
2. Related Art
A light-emitting device utilizing light emission from an electroluminescent element (light-emitting element) has attracted attention as a device for lighting or displaying an image.
In recent years, in the development area for a light-emitting device, the research and development of a light-emitting device capable of displaying a high quality full color image has been accelerated to secure a market of display devices for various information-processing devices such as a TV set or a car navigation system.
In order to obtain full color image from a light-emitting device, it is required that regions exhibiting respectively at least three primary colors of red (R), green (G) and blue (B) are independently provided so as to emit light at the right time.
Various methods have been developed to provide the foregoing regions for exhibiting three primary colors. One method for providing the foregoing regions is forming layers, each of which contains light-emitting compounds displaying different colors, at different sites, thereby providing light-emitting elements each containing one of the layers independently.
In case of using the foregoing method, light-emitting compounds are required to be selected for the respective emission colors. Therefore, light-emitting materials that exhibit light emission over various wavelength ranges have been developed.
For example, as a material exhibiting reddish emission, a bis-4H-pyran derivative as disclosed in Japanese Published Unexamined Patent Application No. 2001-19946 has been developed.
However, some of the bis-4H-pyran derivative disclosed in Japanese Published Unexamined Patent Application No. 2001-19946 are difficult to be formed into a film by vacuum vapor deposition since they are easily carbonized during vapor deposition.
In the case that such light-emitting material as are easily carbonized is used, a tarry substance is liable to be attached to an evaporation source. Accordingly, the exchange frequency of an evaporation sources is increased. As a result, there arises a problem that more light-emitting material for deposition is needed, and so the efficiency in the use of the material becomes worse. Further, there may arise another problem that good luminescence properties cannot be obtained due to a carbonized light-emitting material, or the like.
Therefore, it has been required to develop a light-emitting material that is not only be able to exhibit light emission with good luminescence properties, but also be easily applied to vacuum vapor deposition.